In recent times, there has been a proliferation of medical and other infectious waste materials from various hospitals and health centers, including clinics and doctor's offices across the country. In many cases, current disposal methods are complicated, inefficient and expensive.
Clearly, there is a need to develop a simple, efficient and less expensive method to detoxify biological and medical waste.
Regarding a seemingly unrelated subject, passenger cars and trucks on highways wear out tens of millions of tires each year. Disposal of these used tires has become a major environmental problem. A high proportion of the weight of a tire consists of carbon that reinforces the rubber in both the tread and sidewalls. Tires also contain large amounts of oil and significant quantities of steel, wire and/or fiberglass or polyester cord. All of the components are expensive and require great amounts of energy in their manufacture. Processes that allow economic recovery of these materials from tires or their conversion to other useful products from the huge stockpiles accumulating around the country are very desirable. Unfortunately, the very characteristics that makes tires long lasting and safe on the road (i.e., durability, resistance to puncture and slicing, and resistance to decomposition at moderate temperatures) combine to make tires exceptionally difficult to recycle.
The prior art teaches that rubber tires can be pyrolyzed in the absence of air at temperatures of between 600.degree. F. and 1700.degree. F. (depending on quality and ratio of recoverable material desired) to produce oil, gas and a solid residue that is carbonaceous in nature.
U.S. Pat. No. 3,722,403 issued to Longo discloses a compactor for compacting a slug of material. Material entering from an open hopper is compressed by a semi-circular faced horizontal ram. A vertical ram then expels the material downward into an unsealed container. This is a true refuse compactor for reducing bulk refuse such as garbage to facilitate further handling.
U.S. Pat. No. 4,201,129 issued to Matthys discloses a machine for charging a furnace with scrap fuel. An open hopper, whose bottom opens into a horizontal tubular portion, is filled with scrap. One wall of the hopper acts to move fuel into the bottom of the tubular portion. The opposite wall is pivotably connected to the base of the hopper which, when lowered, forms the upper wall of the tubular lower body. A sliding gate which provides a seal between the charging hopper and firebox is opened, then a ram located in the tubular portion horizontally forces the scrap down the tube into the firebox. The ram is retracted, the gate is closed and the opposite wall is raised, thus completing the cycle.
U.S. Pat. No. 3,815,521 issued to Panning discloses a combined shredder and incinerator apparatus. Loose material is received and shredded. The shredded material is then moved into position by a bottom wall which pivotably swings upward, moving the shredded material into a space defined by a top cover and two side walls. The material is fed into an incinerator by a horizontal ram.
Both of the aforementioned furnaces operate using combustion, not pyrolysis. Each discloses a method of compacting loose, relatively bulky material into a variably compacted state that can then be forced into a furnace or incinerator, for complete combustion. In the two above devices, a partial seal is accomplished due to the inherent pressure drop across the passage through which the materials are forced into the furnace or incinerator. Due to excess air deliberately introduced into the furnaces and incinerators, any additional air that might leak past the feed fuel would have little adverse effect. Accordingly, no air tight seal is required in these systems.
U.S. Pat. No. 4,507,174 issued to Kutrieb discloses a pyrolysis chamber wherein whole tires are heated to approximately 800.degree. F. by radiant energy emitted from radiant tubes passing through the reaction chamber in combination with convection of the product vapor within the chamber. The chamber produces char, wire, fiberglass, oil and gas. This is a batch process where each load is completely pyrolized. The system then shuts down and is allowed to cool. Solid residue is removed, and the chamber is reloaded for a new cycle.
U.S. Pat. No. 4,647,443 issued to Apffel, discloses a process for recovering carbon black, oil and fuel gas from whole, non-shredded, passenger car and truck tires. The tires are first cleaned and then preheated with super-heated steam. The process is divided into a first and second phase. The whole uncompressed tires are loaded into a reactor chamber through a series of airlock gates. The whole tires are then pyrolyzed leaving oil, gas, char, steel and fiberglass cord. The reaction chamber is heated by radiant energy emitted from radiant tubes passing through the chamber as well as by convection of the product vapor within the chamber. With this type of gate arrangement, at a minimum, a volume of gas equal to the volume of a tire escapes to the atmosphere; an equal volume of air is introduced to the reactor with each inserted tire.
U.S. Pat. No. 4,217,175 issued to Reilly discloses a pyrolysis system for pyrolizing/combusting municipal solid waste. An inward tapered nozzle is provided in which a plug of waste forms a seal to prevent air from entering the reactor or vapor from being released into the atmosphere.
In other pyrolysis plants, tires and or other refuse are generally required to be physically broken apart into smaller pieces or fragments. Commercially available tire disintegrators include slicing machines, hammer mills, debeaders and manglers that have been adapted for tire reduction from other industries. The materials from which tires are made, such as steel reinforcing and carbon, make them very difficult and expensive to disintegrate.
U.S. Pat. No. 4,732,092 issued to Gould operates in a continuous mode using shredded refuse, including tires, to produce solid and vapor products similar those produced in the first phase as disclosed by Appfel. A ram feeder is combined with a gate to provide a feed assembly. However, this is a combined pyrolysis and combustion system, so an air tight seal is not critical.
U.S. Pat. Nos. 4,402,791 and 4,401,513 issued to Brewer disclose devices to pyrolize shredded tires producing solid and vapor products in a batch mode as is taught by the aforementioned Kutrieb patent.
The present invention has similarities to each of the above mentioned patents. However, it contains significant improvements therein, which improve both the efficiency and safety of the process of treating whole tire feed-stocks or infectious waste.
It is an object of this invention to provide a system for feeding tires and medical waste to a substantially air tight pyrolyzing reactor and for removing the products of the pyrolytic reaction on a continuous, safe basis.
It is another object of the present invention to provide a system for preheating tires directly using waste heat contained in spent stack gas before the tires enter the pyrolyzing chamber or reactor.
It is a further object of the invention to provide a system of pyrolysis that is both safe and energy efficient, and further wherein the process generates a surplus of fuel gas necessary to power the process itself within applicable laws and environmental regulations.
It is also an object of this invention to provide a pyrolyzing system in which the tires themselves, or cartons of medical or infectious waste, form a seal or plug at the front end of the apparatus and a plug at the outlet formed by a column of solid residue, including crushed char, to prevent toxic gases from escaping and to prevent air from entering the reactor. In this way, an oxygen free environment is maintained for the pyrolysis process, thus improving the safety of the system and bringing the system into compliance with safety regulations and applicable laws.